Impact damage protection mechanisms for elastomer-coated concrete

Cost-efficient strategies for protecting structural elements against the effects of explosive detonations are of interest for vulnerable infrastructure. Dynamic loading due to both blast pressures and impact from fragments are of concern. This investigation focuses on the protection of concrete structural elements against impact damage. A recent experimental study by the authors demonstrated that an elastomer coating can provide a significant impact mitigating effect when applied to the impacted face of a concrete substrate. Preliminary numerical results have indicated that the elastomer serves to alter the details of damage initiation in the concrete, though there remains a limited understanding of the protective effects at play. In this work, a numerical investigation is performed to determine the mechanisms of impact damage initiation exhibited by a concrete circular cylinder of diameter, 100 mm and height, 100 mm when impacted by a 0.1 kg circular cylindrical (i.e. blunt) projectile, travelling at velocities in the range 5–150 m s⁻¹. The influence of applying a 5 mm elastomer coating on these damage mechanisms is assessed. At the lowest impact velocities, the concrete remains undamaged, though the sub-surface stress state is influenced by the polymer coating. At higher impact velocities, two distinct damage initiation mechanisms are observed. Damage Mechanism 1 is characterised by immediate, severe concrete damage initiating under the indenter corner. Damage Mechanism 2 is characterised by more diffuse, sub-surface damage. Adding a polymer coating serves to shift damage initiation from Damage Mechanism 1–2, delaying the onset of severe concrete damage. Simplified 1D and 2D numerical models are employed to interrogate how the elastomer achieves this effect. Two protective effects are identified: (i) a temporal effect causing a reduction in the magnitude of peak acceleration and an increase in contact duration between projectile and target and (ii) a spatial effect where the stress concentration under the indenter corner is removed.